1. Field of the Invention
The present invention relates to a process for the production of a colored resin composition used for coloring a thermoplastic resin and a colored resin composition thereof. Further, the present invention relates to a colored resin molded article, a coating composition and a pigment resin composition for recording information which are obtained from a colored resin composition obtained according to the production process of the present invention.
2. Prior Arts of the Invention
Conventionally, there is used a powdery dry color obtained by mixing a pigment with a dispersant which is solid at room temperature, a liquid color or paste color obtained by dispersing a pigment in a dispersant which is liquid at room temperature, a pellet-like, flake-like or bead-like colored pellet (sometimes also called a colored compound) obtained by dispersing a pigment in a resin which is solid at room temperature or a master batch as a colored resin composition used for coloring a molded article of a thermoplastic resin or for producing a colored resin molded article. The master batch has a common feature with the colored pellet in that these are obtained by dispersing a pigment in a resin which is solid at room temperature. However, there is a difference between the master batch and the colored pellet. The colored pellet itself is directly molded without being diluted with a resin for dilution or a resin for a molded material (that is, the concentration of a pigment is adjusted to the concentration of a molded material as an end product). In contrast, since the master batch contains a pigment in a higher concentration in comparison with the colored pellet, the master batch is diluted with an appropriate thermoplastic resin (a resin for dilution or a resin to be colored) before the molding. From this respect, the master batch and the colored pellet are different from each other.
These colored resin compositions are properly selected and used in consideration of their features depending upon an intended use. Among these colored resin compositions, the master batch is preferably used in view of easiness of handling and protection of a work environment when used. The required performances of the master batch are that the master batch has a high concentration of a pigment and that the influence exerted upon various physical properties of a thermoplastic resin to be colored, such as heat resistance or strength, is small. As a precision-improvement and a speed-up in the molding of a polyolefin resin advance, in addition to these requirements, the high dispersibility of a pigment has come to be required as compared with before.
As a dispersant for imparting a pigment dispersibility to the master batch, there are generally used stearic acid; metallic soaps such as zinc stearate, magnesium stearate, aluminum stearate and calcium stearate; ethylenebisamide; hydrocarbon waxes such as polyethylene wax and polypropylene wax; and derivatives of these such as waxes formed of an acid-modified material or a hydroxyl-group-modified material.
However, when the production of a molded article requires a high-degree pigment dispersion, e.g., a high-speed spinning at a diameter of ten-odd microns or a film molding is carried out, the use of the above dispersant can not give a sufficient dispersion effect.
Thus, in JP-A-7-53772 publication, the compound of the following chemical formula is used as a dispersant for a colored resin composition,CH3—(CH2)x—CH2—O(CH2CH2O)nH
wherein x is 28 to 48 (average) and n is 1 to 16. While the use of this dispersant has given a finer result as compared with a conventional product, a thread breakage while spinning, the clogging of a filter of a melt-spinning machine and blobbing on a film surface still occur because of a poor pigment dispersion in some cases. When a molded article further needs to have higher mechanical and physical strength even if a high-speed spinning or a film molding is possible, it is impossible to impart a practically sufficient strength to the molded article in some cases.
In recent years, a high-degree dispersion of a pigment or an incorporation of a functional material in a master batch is increasingly required so that a variety of studies are made. As one solution, the use of water increases. That is, it is a method using water as a dispersion assistant, in which a pigment or a dispersant and a thermoplastic resin are mixed in the presence of water and then the water is removed to obtain a colored resin composition. This technology can be widely applied and it can be broadly divided by the amount of used water. For example, there are disclosed a method described in JP-A-6-143253, JP-A-6-148937 and JP-A-7-233275 in which a small amount of water is added as a dispersion assistant, a method described in JP-A-51-50952, JP-A-57-186758, JP-A-59-1538, JP-A-61-126139, JP-A-62-161861, JP-A-2-175770, JP-A-2-227469, JP-A-5-341569, JP-A-9-204069 and JP-A-10-279877 in which water is contained as an aqueous cake of a pigment, a method described in JP-A-7-247367 and JP-A-8-302092 in which a dispersant or a dispersion resin is converted into a water-soluble dispersant or a water-soluble dispersion resin and the water-soluble dispersant or the water-soluble dispersion resin is used as a water dispersion, and a method described in JP-A-63-43960, JP-A-10-10799 and JP-A-2000-17083 in which a pigment is used as a solution of a water dispersion. However, the method adding water in a small amount or the method using a paste requires a kneading machine having a strong shearing force similar to a kneading machine required when a dry pigment is used. In addition to this defect, these methods do not accomplish a great performance improvement in dispersibility although the necessity for removing the added water is added. On the other hand, the method using a water dispersion containing a large amount of water does not require a kneading machine having a strong shearing force. However, the above method can be practically applied only when a specific resin is used. Therefore, a produced colored resin composition is poor in general versatility under the present situation.